Ultrafine particle (UFP) emissions of aircraft may cause serious adverse health effects. The current study considers the transport of UFP emissions via the wake vortices generated by aircraft approaching Frankfurt Airport down to the ground. For this purpose, the fast-time Probabilistic Two-Phase wake vortex prediction model P2P has been enhanced for the prediction of the transport of a passive tracer with the descending wake vortex oval. The parameterisation of tracer transport considers the associated turbulent mixing processes of the vortex oval with its environment and the detrainment into a secondary wake, both causing the dilution of the tracer. The study considers the wind conditions prevailing in the year 2019 and the respective traffic mix of Frankfurt Airport. The presented results comprise the dwell times of the wake vortices reaching the ground, the corresponding passive tracer concentrations and the UFP numbers. The computed UFP numbers are set into perspective to UFP number concentrations measured at a distance of about 4 km to the airport using a mobile ground measuring station. It is found that the UFP emissions of approaching aircraft are small compared to other sources at the airport. Even UFP counts of direct wake vortex hits on the ground are on the order of the background concentrations. At a distance of 9 km from the runway ends the UFP numbers drop to less than 1% of the maximum ground immissions occurring near the runway thresholds. Left wake vortex generated over the runway by DLR research aircraft ATTAS visualised by red smoke (left) and detail of UFP number distribution at the ground near runway 07R of Frankfurt Airport (right). • Transport of ultrafine particle emissions (UFP) via wake vortices down to ground. • Consideration of wind conditions and traffic mix of Frankfurt Airport in 2019. • UFP emissions of aircraft approaches are small compared to other sources at airport. • UFP counts of direct wake vortex hits are on the order of background concentrations. • At 9 km from runway UFP numbers drop to less than 1% of maximum ground immissions.
Frank Holzäpfel (Wed,) studied this question.